Design Concepts for the Rube Goldberg Machine
The next project I am working on now is the design of a Rube Goldberg Machine. These machines are built to complete a simple task in an extremely overcomplicated way. The purpose of these machines is not to be practical or efficient in the manner it completes its task, as seen with the last few projects discussed here, but simply to be fun and entertaining.
This is a nice change and gives a lot of free reign on what I can do with my design. It doesn’t however mean that there wont be careful design and planning involved as I’m sure anyone who has ever built one of these would agree. Here I am going to be going through a few of the components I have designed for the machine and some calculations I made. These calculations will give me a better understanding of how the components work and how the can be best implemented when I eventually put everything together at the end. The plan is also to use some of the different components I have built and designed so far in the machine as well, including the ping pong ball launcher and of course the Tumbller itself.
So far I don’t have a grand plan of how all the elements I’ve been working on will come together in the end. I am excited though to see how the machine will end up. For now, I’m going to take you through the different components I have gathered and designed and how they work.
First of all I hunted around the house for some staples that almost always appear in any Rube Goldberg machine. These included some kind of ball and rail and then also a pully mechanism. Luckily I had a lot of ping pong balls lying around the house that I ordered for the Launcher designed previously and I found some railing in my shed which fit the balls pretty well. This is already a pretty good start as it will allow me to move a ping pong ball around the room, from component to component. At least that is the plan.
I also managed to hunt out two pulleys which I cable tied to the skylight and ran a string through. I still am not entirely sure what I will use this for but at the moment I am thinking to have it lower down an object in front of the Tumbller to activate its ultrasonic sensor. I quite like this idea so this could well end up in the final set up. An image of the pulley system can be seen below.
Another common component seen in Rube Goldberg Machines is some sort of projectile launcher. This is often a highlight of the machine and so I was always going to add this to mine. The obvious choice for the job was my ping pong ball launcher, seen below.
If you have been following my blog posts you will know that the launcher hasn’t always been accurate in firing ping pong balls the correct distance. This was clear when viewing my obstacle course navigation attempt where I both undershot and overshot my target by some distance (although I did manage to get one ball in). This is almost completely due to me and not the launcher as the force I applied obviously varied considerably. I did want to do some calculations though to find out the correct forces required and hopefully get the launcher firing a lot more accurately.
For anyone not interested in lots of numbers and equations feel free to skip down to the End of Launcher Calculations.
Launcher Calculations
As we know from a previous launcher post, ‘Choosing the Design’ , the force of a spring can be very easily calculated and predicted due to Hooke’s Law. This states that the force generated by the spring is directly proportional to its displacement, by a factor called the spring constant. A link to that post can be found here. I’m hoping to be able to calculate the required spring displacement to launch the ball a specific horizontal distance.
I went about this with the equations below used to predict the trajectory of a projectile. These equations don’t take drag and friction into account, which in this case is not the worst assumption as the launcher will be used indoors and the ball is small and quite aerodynamic.
To find values for these equations I did another test with the launcher. This can be seen below.
For the test I made the horizontal distance = 2.55m and the launch angle = 55 degrees, as measured with my protractor. I then measured the flight time to be approximately 0.65 seconds. With this information I completed the following calculations to find the initial velocity of the ping pong ball.
I then subbed this value into the formula for kinetic energy, as well as the mass of the ping pong ball which I found to be 3g = 0.003kg.
Then I equated kinetic energy with with work and divided by the horizontal distance to find the force on the ping pong ball. For the calculation here I am assuming that the distance is purely horizontal, which is not actually the case as there is a significant vertical distance in the balls flight.
Finally coming back to Hooke’s law, I subbed in the spring coefficient I found to be 172.3 N/m in the previous blog post I linked earlier. I divided the force on the ping pong ball by two due to the two springs in the launcher. This then gave me my value for the required spring displacement.
Unfortunately the result however seems to be quite off with the spring displacement distance translating to be 0.081 mm. It would need to be a pretty insanely powerful spring for this to be anywhere accurate. I do apologise if you took the time to read through all of that just for a dud result. Possible errors within the calculations would of course be purely taking the horizontal distance into account. Another consideration is of course that the ping pong ball is not receiving the total force generated by the springs as there is a whole lot of friction within the launcher and contact between the ball and the launcher is also not perfect.
The analysis was still good here, I will just have to work experimentally to find the correct spring displacement length. I plan on drawing a visible marker at this length on the launchers inner element so that I will know how far to pull it back. This should increase the accuracy and consistency of the ball flight significantly.
The calculations were also not completely in vain as I was still able to calculate the vertical distance of the projectile which could come in handy when designing the Rube Goldberg.
This result seems very accurate when looking back at the video.
End of Launcher Calculations
Besides the few components I have already mentioned there are a few other pieces of the puzzle in the works for the Rube Goldberg Machine. These were actually quite fun to come up with and put together.
Mallet Projectile Launcher
The little brother of the ping pong launcher was simple enough to build. It involved drilling a hole through the wooden handle of the mallet and fixing it to the end of a plank of wood with two nails. This allows it to rotate about the end of the handle.
The mallet hits the elevated edge of a thin metal strip, on the other side of which is a ping ping ball. The cork underneath allows the metal strip to act as a lever and fires the ball into the air.
Nothing too complex but lots of fun! Check out the video below for a quick demonstration.
Buoyancy Device
This contraption was another fun one to build. It is probably easier to explain though once you have seen the short demo a few times.
The basic idea was for a ping pong ball to sit behind a thin piece of plastic running through the platform underneath the ball. The plastic piece is however attached to corks floating on water in the bottle. Once the water is let escape (I still haven’t decided how this will happen) the plastic piece drops down with the corks and frees the ping pong ball to roll down the rail.
This one definitely fits the bill in terms of overcomplicating the simplest task.
They are all the updates for now. I am happy with how the the machine is progressing so far and really looking forward to finishing it up and seeing the end result.
I hope you enjoyed this update. More is coming soon.
